In order to promote recovery of the morphology and function of living tissue removed by tumorectomy and the like, there is a desire for the development of a new treatment method based on cell transplantation, in addition to the conventional replacement techniques that use biomaterials. In recent years, with regard to bone tissue and the like, regenerative therapies that use tissue stem cells such as bone marrow-derived mesenchymal stem cells are approaching the practical stage (see NPL 1). However, bone marrow puncture is necessary to obtain bone marrow-derived mesenchymal stem cells, and it is difficult to acquire the number of stem cells necessary for the treatment. Therefore, there is a desire for a source of stem cells that can be more safely and easily.
At the same time, in recent years, a technique to reprogram the somatic cells and induce them into pluripotent stem (iPS) cells, in which genes respectively encoding OCT3/4, KLF4, c-MYC, and SOX2 are introduced into somatic cells was reported, and innovative techniques have been provided in the field of regenerative medicine (see NPL 1). The progress in iPS cell research is remarkable, and the application thereof in regenerative medicine is drawing attention as a national project.
iPS cells can be produced from the patient's own somatic cells; are free from immunological rejection; and raise fewer ethical issues. Therefore, iPS cells are expected to be put into practical use for clinical purposes. Conventionally, dermal fibroblasts have been primarily used to produce iPS cells. However, it has been reported that iPS cells can also be produced from liver and stomach cells (see NPL 2), peripheral blood (see NPL 3), and extracted wisdom teeth cells. Nevertheless, the conventional somatic cells used for producing iPS cells face the following problems: iPS cell establishment efficiency is low; and such cells do not provide a stable supply source of iPS cells. Further, the conventional somatic cells used for producing iPS cells are also disadvantageous in terms of the burden on the patient, because collection of the somatic cells accompanies surgical invasion of living organisms.
With a background based on such conventional techniques, there is a keen desire for the development of a technique for producing iPS cells with less burden on the patient, and high establishment efficiency.